As the operation speed and power of a generic desktop computer, notebook computer, or MPU device, etc., is stepwise raised, cooling efficiency becomes an issue of extreme importance.
Referring to FIG. 1, an existing cooling fan is usually composed of a shaft assembly (B) pivotally mounted on a frame (A), in which a depression (A1) having an upward and a sideward opening (B1) is centrally formed for receiving the shaft assembly (B) which is radially and outwardly extended to form a plurality of fan leaves (A2) and driven to rotate by an electrical device arranged in the frame (A).
Because the mentioned cooling fan is usually a micro-fan with a small momentum applied for electronic devices, its mechanical efficiency could deteriorate significantly by an incurred turbulence. As indicated by arrowheads in FIG. 2, a clearance could be found between the frame (A) and the shaft assembly (B) to allow the generation of turbulence that would impose an extra resistance on the shaft assembly (B), and also reduce the negative-pressure effect and accordingly the intake quantity of air to consequently result in a degraded cooling effect.